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L. O HOWARD. F-nlomologui and Chi^f of Bureau. 



\Y. w. MOTHERS, 
Entomological Assistant. 


•WaHTOH iwnioin >«,»T|»« OTFKJ <rw 


L. O. Howard. Entomologist and Chief of Bureau. 
C. L. Mabxatt, Entomologist and Acting Chief in Absence of Chief. 
It. S. Clifton, Executive Assistant. 
W. P. Tastet, Chief Clerk. 
F. H. Chittenden, in charge of truck crop and stored product inset investigations, 
A. D. Hopkins, in charge of forest insect investigations. 
W. D. Hunteb, in charge of southern field crop insect investigations. 
F. M. Websteb, in charge of cereal and forage insect investigations. 
A. L. Quaintance, in charge of deciduous fruit insect investigations. 
E. F. Phillips, in charge of bee culture. 
D. M. Rogers, in charge of preventing spread of moths, field icork. 

ROLLA P. CUBBIE, in charge of editorial trork. 

Mabel Colcord, in charge of library. 

ClTBUS Fbuit Insect Investigations. 
C. L. M\ur. \n. in charge. 


C. E. Pembebton, II. L. Sanfobd, entomological assistants. 
Beulah M. Boss, preparator. 
J. G. Sandebb, collaborator. 

Circular No. 168. Umua April it 

United States Department of Agriculture, 

L. O. HOWARD. Entomologist and Chief of Bureau. 


By W. W. ITothebs, Entomological latUtant. 

Citrus trees in Florida are subjed to injury by four species of 
white flies only two of which, however, the citrus white fly (Aley- 
U. & II.) and the cloudy-winged white fly (Aleyrodes 
mtbifera Berger), do sufficienl damage at the present time to de- 
mand remedial measures. Of the two species considered the citrus 
white fly is by far the most injurious. 


The citrus white fly is an introduced pest, having been brought 
to (his country from Asia some time prior to L879. Since it< intro- 
duction it has spread over the entire citrus region of the Mate and 
westward throughout the Gulf region. At the presenl time it infests 
fully 60 per cenl of the groves in Florida. It occurs on some 10 
apecies of tree-, and shrubs, the most important hosts being the China 
trees, Cape jessamine, privet, and various species of citrus. Of 

native plant- the only two which have been reported as being Seri- 
ously infested are the prickly ash and wild persimmon. 

I.I IK BOSTOBl AND II \l'.i is. 

Th completing it- life cycle the citrus white fly passes through 
four stages, viz, egg, larva, pupa, and adult. 

Th,- egg. — To the unaided eye the eggs appear as minute particles 
of whitish dust. They arc deposited on the underside of the leaves. 
To indicate the size of these eggs it has been estimated that ih 
place. 1 end to end would measure 1 inch, whereas 1 square inch 
would contain about 35,164, placed side by aide. When examined 



under a magnifying glass they resemble kernels of wheat in shape 
and appear as smooth, polished, greenish-yellow objects. After 
they are deposited, from 10 to 12 days are required for the eggs to 

The larva. — The newly hatched larva of the white fly is active, 
resembling that of a scale insect. After crawling for several hours 
it settles on the underside of a leaf, inserts its beak, and begins to 
take nourishment by sucking the juices of the plant. To reach 
the pupal stage it sheds its skin three times, the legs being reduced 
to mere rudiments after the first molt. The duration of the larval 
stages is approximately 23 days. 

Hie pupa. — The pupa closely resembles the last-stage larva, but 
at maturity is thicker, more rounded, with a bright red spot on the 
back. From 3 to 8 days before emergence the eyes of the adult be- 
come visible. The duration of the pupal stage varies from 13 days 
in the summer to a maximum of 304 days during the fall, winter, 
and spring. The larvae and pupa? secrete honeydew, which drops on 
the leaves and fruit, furnishing nourishment for sooty mold. 

The adult. — The winged adults emerge from the pupal cases, which 
remain attached to the leaves. They collect most abundantly on the 
new growth and there they deposit their eggs. A single female has 
been known to deposit as many as 250 eggs, but the average is not 
more than 150 for each individual. The average life of the adult 
is 10 days. 

Seasonal history. — The citrus white fly passes the winter in the 
pupal stage, the adults of the first brood appearing in maximum 
numbers in March or early April, depending upon the season and 
location. After the practical disappearance of the last brood there 
is a period of about six weeks when adults are scarce. The second 
flight, or brood, of adults takes place in June. There is no marked 
absence of adults between the second and third broods, owing to the 
overlapping of these broods. The third brood reaches maturity in 
August, when the third and last flight of adults takes place. The 
eggs deposited by this third brood develop to the pupal condition 
and thus they remain on the leaves until the following spring. The 
third brood is by far the most numerous, and the larva? and pupa? 
following this flight, by the extraction of sap and the excretion of 
honeydew upon which sooty mold grows, cause the greatest damage 
to citrus trees. 


The cloudy-winged white fly may be distinguished from the citrus 
white fly as follows: The eggs of the former are dark and have a 
reticulated surface. Those of the citrus white fly are greenish yellow 

sn: ! i OB WHITE nil- in ii OBIDA. .5 

iiml smooth. The pupa case <>f the cloud] \% i mri-tl white fly is thin 
and membranous and collapses after the emergence of the adult, 
while thai of the citrus white flj retains its shape indefinitely. The 
adults are easily distinguished; the cloudy winged white fly has dark 
markings <«n it- wings, while the wings of the citrus white fly are 
pure white. The broods of the cloudy-winged white fly appear about 
a month later than those <<( the citrus white fly. 


The injury caused by the citrus and cloudy winged while flic- i- 
much greater than is generally supposed. Tin- damage occasioned 
by tin' loss of sap is considerable anil 1- a serious 'train mi the tree, 
hut i- of secondary importance to the damage caused by the sooty 

mold which follows the white fly. 

The sooty mold affects both the fruit ami leaves, blackening the 
former ami covering the upper surface of the latter with a dark- 
brown coating which excludes the sunlight anil clogs ami checks the 
growth. The reduction in yield from tin' white Hie- ami sooty mold 
is variously estimated to he from 25 to 50 per cent. 

If the sooty moli I form- a coating on the upper half of the orange, 
the rind underneath it may remain green indefinitely, while the lower 
half of the fruit becomes well colored. The retardation of ripening, 
delaying as it does in some cases the time when the fruit i- market- 
able anil materially increasing the percentage of culls, causes further 
loss, which i- very conservatively estimated to range from 2 to ."> per 
rent of the value of the crop. 

It is customary to dean fruit noticeably affected with sooty mold. 
The process of cleaning causes many mechanical injuries which afford 
entrance to the -pore- of the blue mold with its resulting decay. 


White Hies may he controlled in two ways: (\) By subjecting the 
infested plant- to the fume- of hydrocyanic-acid gas, or (2) by 
spraying with a contact insecticide. The latter method only i- con- 
sidered in this paper and has the advantage of being comparatively 
inexpensive and adapted to grove conditions in Florida. 

ait\i; \ i OS FOB -I'K O i\>.. 

Tn spraying, an extension rod, varying from s to 10 feet in length, 
should be supplied with each line of hose, the length depending upon 
the heighl of the tree-. This roil ma\ be an ordinary bamboo pole 

or a -mall <:as pipe. The former i- more suitable for this work in 
that it i- lighter ami more easily handled after becoming wet. 



A cut-off should always be inserted between the extension rod and 
the hose. This will enable the operator to cut off the spray at any 
time, either when going from tree to tree or in order to clean out the 
nozzle should it become clogged. If a power sprayer is used it is 
also necessary to insert a cut-off between the hose and pump, which 
would relieve the pressure on the hose in case of a break. A cut-off 
inserted at this point also makes it possible for a machine to be fitted 
with any number of leads of hose which the work may require. 

The hose should be from three-eighths to one-half inch in diameter, 
of the very finest quality, and able to withstand such pressure as the 
methods of application may require. If a power sprayer is used the 
hose should be a good quality 7-ply; with reasonable care this will 
stand up for a season under 150 or 170 pounds pressure. If a barrel 
pump is used, 4-ply will be sufficient, but even for this the 7-ply is to 
l)c preferred and will be found cheaper in the long run. In our ex- 
perimental work leads of hose 50 feet in length have been found more 
satisfactory than shorter ones. With long hose both mules and 
machine may be kept out of range of the spray. Then, too, when 
using two leads of hose it will be possible, if the hose is long, to 
progress uninterruptedly on both sides even though there may be a 
tree missing in one row or the other. In spraying the larger trees 
long hose is essential in order that the sides of the trees away from the 
machine may be reached. 

To secure satisfactory results the application should be thorough 
and with sufficient force to break up the liquid into a fine mist. The 
kind of pump to be used should be governed by the size of the grove 
and other conditions. A barrel pump will serve every purpose if the 
trees are low and only a small amount of spraying is required. For 
larger operations a gasoline-power outfit will give better satisfaction. 
For Florida such an outfit should be light in weight, with 6-inch tires 
and an engine of not less than two and one-half horsepower. To keep 
the machinery free from sand the engine should be provided with 
canvas curtains. 

To obtain satisfactory results it is necessary to have the proper 
equijunent for applying the insecticide. Much of the prejudice 
against spraying for the control of white flies arises from the ineffi- 
cient results due to improper equipment. 

Since the insects congregate on the underside of the leaves the 
spray should always be directed upward. To accomplish this one 
should use a straight nozzle attached to an elbow which makes an 
angle of approximately 45 degrees or. better still, an angle nozzle 
which will not get entangled in the foliage and branches. A nozzle 
which emits the spray in the form of a cone haying an angle of about 
90 degrees has been found to be very efficient, whereas a flat or solid 
stream will not give satisfactory results. 

BPRAYING FOB w 1 1 III I I 1 1 B in PLOBIDA. i> 

I n i \\ PO M'l'i v i in BPB \ V. 

Tn spraying for control of white flies the method of application 
is the same when using either ;i barrel pump or :i power outfit. 

In applying the spray the operator should begin on the far side 
dt" the tree and work around to the point nearest the machine I he 
second half of the tree should be handled in like manner, If two 
operators are at work on the same tree they should l><>ih l»'L r m :ii t- 1 » < * 
point farthest from the machine and proceed until they meet. 

Tin' spray should be applied in tin' tree in a systematic way. The 
operator should begin at the base ami work (<> the top, inserting the 
rod among the branches bo a- to spray the center of the tree. Tin' 
entire tree may be thus sprayed in sections, tin' operators proceeding 
alternately from the bottom t<> the tup and from the top t<> the bot- 

lom. 'In prevent kinks from appearing in tin- hose tl perator, in 

moving from tree i<> tree, should never make a complete turn. In 
case kinks appear thej should be immediately taken out by turning 
tin 1 -pray rod ami qoI by pulling the hose. 

BPB \ V M i\ n KB. 

It i- important thai tin- insecticide used should kill all the inserts 
hit by the spray. Emulsions of various heavy mineral oils have 
been found to give the | M .-t satisfaction. While petroleum fuel oil, 
or "crude oil." and distillate, or <;a> oil. will give good results, yet 
the paraffin oil-, known also a- lubricating oils, having a specific 
gravity of from 24 to 28 Baume* have been found to possess cer- 
tain qualities which make them superior as base- for an insecticide 
against the white Hie-. The following formula ha- given highly 
satisfactory results : 

Foumi i s No. 1. 

Whale-oil soap 8 pounds, or] pallon. 

Paraffin oil. 24" or 28 Baume 2 gallons. 

Water 1 gallon. 

DIIU' nonS I oi! PR] PARATIl 

Tn preparing the stock mixture the soap should be put into a re- 
ceptacle of about 5 gallons' capacity and the oil should then !><• added 
very slowly while the mixture i- being vigorously stirred. It is 
important that the oil he added in -mall quantities at first and also 
that the stirring he sufficient to keep the oil and soap in the form 

of an emulsion after each addition of oil. Thus at first about a 

pint of oil should he added to the -oap and the mixture stirred until 
no free oil appears. As the amount of oil i- increased it should 
always he stirred or mixed thoroughly before the next addition is 


made. After the required amount of oil has been added and after 
free oil has ceased to appear on top of the soap, the water is slowly 
poured in, about a quart at a time. To determine whether the mix- 
ture will form a perfect emulsion add a little of it to soft water, and 
if no oil floats, the mixture is perfect and may be used for spraying. 
The presence of floating oil indicates an imperfect mixture and 
results from adding the oil too suddenly or from insufficient stir- 
ring. This condition may be remedied by the addition of more soap, 
which is preferable to throwing away the entire mixture. 

For spraying orange trees 1 gallon of the stock mixture pre- 
pared as just described to 50 gallons of water, or use the entire 
amount to make 200 gallons of spray material. This dilution con- 
tains approximately 1 per cent of oil, which is the maximum strength 
required for white flies and the purple scale. For three-fourths of 
1 per cent of oil add 1 gallon of the stock mixture to 66 gallons of 
water, and to obtain one-half of 1 per cent add 1 gallon of the stock 
mixture to 100 gallons of water. 

Many alterations may be made in the foregoing formula. The 
quantity of soap will depend largely upon the time consumed in 
adding the oil and the amount of stirring accompanying this process. 
The amount of soap is lessened if the stirring is uniform and if 
ample time is taken in the preparation. Petroleum fuel oil, or 
"crude oil," and distillate, or gas oil, may be used instead of the 
paraffin oil, but in these casas a mixture of about twice the strength 
will be needed to kill the insects. The amount of water is unim- 
portant, since the emulsion should be perfect if either 1 or 4 quarts 
be added. The only thing to be remembered is that the diluted spray 
should contain the required percentage of oil. 

The following formula from Farmers' Bulletin Xo. 172, page 17, 
has also been found satisfactory : 

Formula Xo. 2. 

Water ( boiling) gallons.. 5 

Distillate.' 28° Baunie do 5 

Whale-oil soap pounds.. 1J 


Dissolve the soap in hot water and add the distillate, thoroughly 
emulsifying by means of a pump until a rather heavy creamy- 
yellowish emulsion is produced. For use against "die white fly dilute 
1 part of the stock emulsion with 25 parts of water. This dilution 
will contain about 2 per cent of the oil. 

1 Tin' term " distillate " ia commonly given in California to a form of petroleum widely 
ased for spraying purposes. 

BPRAYING FOR whim iiiis i\ FLORIDA- 7 

PBOPRIS1 w:v I NSW i i< IDH, 

There are Beveral articles on the market under the bead of miscible 
oils which when properly applied will give satisfactory results. 
These, however, should not contain sulphuric Bcid, rosin oil, or 
carbolic acid. 


- far as the effed of various insecticides on the trees and fruit 
is concerned it is safe to spray at any season "f the year except dur- 
ing the blooming period. It" the application is made during the 
winter, it will be found much more convenient t<> Bpray after the 
removal of the fruit. The insecticide will do no injury to the fruit 
itself, hut its presence <>n unwashed fruit may prose objectionable 
to the consumer. It can also be applied during the summer or rainy 
>ii, l>ut spring, early fall, or winter applications are preferable 
in that the benefice] parasitic fungi are not affected by the inseoti- 
i ide during these seasons. 

So far as the effect on the various stages of the insects i- con- 
cerned spraying may be done at any tune. The white fly is in the 
tendered larval stages about two week- after the disappearance of 
the adults of the first brood, ami if spraying is done at this period 
the insecticide can be used at about one half or three-fourths the 
usual strength. 

The grower should aim to keep the white fly below the point 
whore it will do serious damage, and the number of treatments will 
depend upon the thoroughness of the work and the abundance of the 
bisects in the grove at the time of spraying. One thorough spray- 
ing is much more effective than two or three carelessly applied. 

The application of the insect icide should be SO timed as to be effec- 
tive in killing the rust mite (Eriophyes oleivorus Ashm.) and scale 
insects as well as the white flies. Experience has shown that two 
sprayings are sufficient to control the white (lies. One of these can 
be given in the spring, following it by an early fall application, 
or one can he given during midsummer and the second during the 
winter month-. The spring and summer sprays are also beneficial 
in killing the rust mite. Sale insects frequently gain such a foot- 
hold as to demand winter treatment, hut in some instances one spray- 
ing a year has produced clean fruit. 

SPRAYING W \m iv-n n \M> Tin- BUBT KITE. 

The paraffin-oil emulsion spray when used with 1 per cent of 
oil will kill the rust mite and its eir^s and also the purple scale 
{Lipidosapfus beckii Newm.). It is also effective when used 


against the young of the Florida red or "nail-head" scale (Chry- 
somphalus aonidum L.). 


The experiments so far conducted indicate that the oil sprays do 
not possess any fungicidal properties, nor do they affect the bene- 
ficial parasitic fungi in the least. These fungi develop during the 
rainy season, while the scale insects, rust mite, and white flies do 
their greatest damage from September 1 to June 1. The fact that 
these sprays are applied during seasons when the fungi are inactive 
is evidence in favor of such remedies in that the increase of the 
fungi is not directly affected. 

Approved : 

James Wilson, 

Secretary of Agriculture. 
Washington, D. C, January IS, 1913. 

ADDITIONAL COPIES of this publication 
it may be procured from the Superintend- 
ent of Documents, Government Printing 
.Office, Washington, D. C, at 5 cents per copy 


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